Manchester United manager Alex Ferguson has ruled captain Nemanja Vidic out of Sunday's derby at Manchester City after putting his comeback on ice.
Serbia defender Vidic, 31, was due to return after three months out with a serious knee injury against Romanian champions CFR Cluj in the Champions League on Wednesday.
Vidic trained with United on Tuesday morning ahead of the Group H encounter at Old Trafford, but Ferguson told a news conference later in the day that the player needed more time before playing again.
"He's not far away and he's training very well, but I think another few days will bring him on better," he said.
"If he doesn't play tomorrow (Wednesday), there's absolutely no chance of him playing in the derby game. I wasn't considering him on Sunday anyway.
"Playing tomorrow would have been a bonus for us and we could take it on from there, but Sunday would be too soon."
Vidic's absence is a setback and comes at a time when United's defensive performances have been criticised.
They have kept just four clean sheets in 22 league and cup games, and conceded three goals in a 4-3 win at struggling Reading last weekend.
"It's a worry, it's a concern," admitted Ferguson.
"If we perform like that on Sunday, then God knows what's going to happen to us. I can't ever remember us conceding so many goals before Christmas."
With United already through to the Champions League last 16, Ferguson is expected to rest several key players ahead of a game that could see his side open up a six-point lead over second-place City if they win.
But Ferguson is ready to gamble with striker Wayne Rooney's fitness as he looks to ensure the England striker -- who has scored eight goals in 17 appearances for club and country this season -- is in peak condition before the meeting between first and second at City's Etihad Stadium.
Rooney pulled out of England's recent friendly with Sweden with an ankle problem, while he has also suffered from a bout of tonsillitis.
"When he is interrupted in a run of games, it takes him several games to get back and that's why he will definitely play tomorrow," added Ferguson.
"Wayne needs to be playing a lot of games to get his match fitness. He is a strongly built lad and when he misses games, it takes him several games to come back. It's just the way he's always been."
Midfielders Ryan Giggs and Tom Cleverley, as well as striker Javier Hernandez, are expected to feature against Cluj, who must better Galatasaray's result at Braga if they are to join United in the last 16.
Youngsters Scott Wootton and Matthew Larnell could make the substitutes' bench.
Meanwhile, Ferguson said Japanese midfielder Shinji Kagawa could return to the squad at the weekend after a knee injury.